As you may recall, Microsoft promised to release Call of Duty not only on PlayStation, but also on other platforms if they could complete their purchase of Activision Blizzard. Nintendo was one of the platforms specifically mentioned, but so far nothing has happened.
However, that doesn't mean Microsoft has forgotten its promise, and if we are to believe Windows Central editor Jez Corden (who has a good track record for insider information), the premiere is just months away. He writes on social media that Call of Duty for Switch is "on the way and hitting milestones," and that the version is "nearly done and launching in a few months."
It is unclear which Call of Duty he is referring to, though. It could be an earlier installment in the series, a collection of some kind, or Call of Duty: Black Ops 7. Perhaps most likely candidate would be their live service title Call of Duty: Warzone. If Corden is right, we should find out more soon - why not at Microsoft's event at the end of January?